Questions

Yes, a promise can be broken without being held.

Blood is a heterogeneous mixture because the blood cells are physically separate from the blood plasma. The cells have different properties than the plasma. The cells can be separated from the plasma by centrifuging, which is a physical change.

Sound is a mechanical vibration and needs a medium for propagation. The higher the density of the medium, the faster the sound travels. So, sound cannot travel through vacuum.

As the sound travels faster in solids than liquids and gases, sound travels faster in the glass than Air and water.

The olfactory system is the only system in which the receptors send their signal directly to the higher brain and bypass the thalamus, which normally acts as a filter for the processes of the lower brain.